(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to form a borderless contact hole to an underlying conductive region
(2) Description of Prior Art
The trend to micro-minituriaztion, or the ability to fabricate semiconductor devices with features smaller than 0.50 micrometers, has presented difficulties when attempting to form narrow diameter, deep contact holes in a dielectric layer, to expose underlying conductive regions. The use of photoresist as a mask for etching of a thick dielectric layer presents selectivity concerns in regards to a fast removal etch rate of the photoresist, in the dielectric layer etching ambient, therefore not allowing only the photoresist shape to be used as the etch mask. Increasing the thickness of the photoresist mask to accommodate the non-selectivity of the etch ambient only reduces the resolution needed to define deep, narrow diameter openings. The use of a hard mask layer, with increased etch rate selectivity to the material being etched, results in additional process cost as a result of the ex-situ removal of the photoresist shape, performed after the photoresist shape had been used to define the desired opening in the hard mask layer. In addition, ex situ removal of the hard mask layer, also results in unwanted additional process cost.
This invention will describe a process for defining a narrow diameter, contact hole opening, in a thick dielectric layer, featuring in situ removal of the defining photoresist shape, after transferring the desired contact hole shape to a hard mask insulator layer. The present invention will then teach a process in which the desired contact hole opening is in situ formed in the thick dielectric layer, followed by an in situ procedure which defines the desired opening in a bottom insulator stop layer, while removing the hard mask insulator layer from the top surface of the thick dielectric layer. This completely in situ, dry etch procedure, allows the attainment of a borderless contact to be realized. Prior art such as Chiang et al, in U.S. Pat. No. 5,922,515, describe a process for forming a deep contact hole in a dielectric layer, using a hard mask layer, however that prior art does not teach the complete in situ, selective dry etch procedure, described in the present invention featuring in situ removal of the hard mask insulator layer during definition of the contact hole opening in a bottom insulator stop layer.
It is an object of this invention to define a narrow diameter, deep contact hole opening, in a dielectric layer, using an in situ, dry etching procedure.
It is another object of this invention to initially define the desired contact hole opening in a hard mask insulator layer, using a photoresist shape as an etch mask, followed by the in situ removal of the defining photoresist shape.
It is still another object of this invention to use the hard mask as a etch mask to in situ define the desired contact hole opening in a dielectric layer, with the selective, in situ dry etching procedure terminating on an underlying stop layer.
It is still yet another object of this invention to in situ define a borderless contact hole opening in the stop layer, again using the hard mask insulator layer as an etch mask, exposing an underlying conductive region, and resulting in the in situ removal of the hard mask insulator layer from the top surface of the dielectric layer.
In accordance with the present invention an in situ, dry etch procedure, used to form a borderless contact hole opening in a dielectric layer, is described. After defining a desired contact hole opening in an overlying hard mask insulator layer, via a dry etching cycle using a photoresist shape as an etch mask, the photoresist shape is in situ removed. Another in situ, dry etch cycle is next used to selectively transfer the contact hole opening, defined in the overlying hard mask insulator layer, to a thick dielectric layer, with the selective dry etching procedure terminating at the appearance of an underlying insulator stop layer. Finally another in situ dry etching cycle is used to define the desired contact hole opening in the underlying insulator stop layer, exposing a portion of the top surface of a conductive region, resulting in a borderless contact hole opening. The dry etching cycle used for the opening of the insulator stop layer also results in the in situ removal of the exposed hard mask insulator layer.